Vulcanization of acrylic resins



Patented June 17, 1952 VULCANIZATION F ACRYLIC RESIN$ William.C. Mast, Philadelphia, Ohessie E. Rehberg, Glenside, and Charles H. Fisher, Abington, Pa., I assignors to the United States of America as represented by the Secretary 01 Agriculture No Drawing. Application August 22, 1947,

Serial No. 770,180

2 Claims. (01. 260-63) (Granted under at act of March a, 1883, as amended April so, 1928; 370 0. G. 757

1 This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described, if patcnted,'may be manufactured and used by or for the Government of the United States of America for governmental purposes With'outthe payment to us of any royalty thereon;

This application is a continuation-in-part of our application Serial No. 595,870, filed May 25, 1945, which has matured into Patent No. 2,492,- 170.

This invention relates to synthetic rubbers prepared from alkyl acrylate polymers and. copolymers.

In'accordance with current practice, the term synthetic rubber is used herein to designate a synthetic rubberlike material which, at ordinary temperature, can be stretched to at least twice its initial length, and will forcibly retract to substantially its original dimensions within a reasonable time thereafter.

It is known that synthetic rubbers can be pro- 0 duced'by vulcanization of certain polymeric substances. As in the treatment of natural rubber, vulcanization ,of these synthetic polymers is a process whereby a thermoplastic, solvent-soluble substance of limited elasticity and high plastic flow is converted toa highly elastic, insoluble material', substantiallyfree 0f plasticflow properties, and relatively insensitive to temperature variations.

'Heretoforethe presence of olefinic unsaturation in the polymeric chain was considered necessary to render'the polymeric material susceptible of vulcanization. Thus a number of synthetic rubbers are produced by vulcanization of unsaturated polymers formed either from butadiene andrelated dienesor obtained by copoly'merization of monomer mixtures comprising at least one diene component.

It is known that thepolymers of methyl acrynot produced when alkyl acrylate pol as polymethyl acrylateand 'polyethylacf heated with sulfur. "We hate at" "Ifi'pt vu zation by heating s cn mymersebn fur and mixtures of suenpeiymersg sulf black, and'some of the standard accelerator used in the vulcanizationbf naturaYrubberI'wlt 'iip ms f results andthe"rrqi et sbci cs defined, is

lack manyof the desirable roperties'f ulcaniz d rubber ar d the bers.

pr duc 'vulcenizcsla k can rplvzn'efs haying enhanced rubberlike properties "mamma of being used in place of rubber. Anotherobiect is to prepare alkyl acrylatepolymjers', tvhic be fl m undfid and mi l ld lls nd eq i men and a standard rubber mold's'to g ve vulcanize like products. A further object isto prqdu thetic rubbers whichfhave light Oils w i n a ners? set,

object of this invention, accordingly, is to natural rubber and some of the previously described synthetic rubbers. A further object is to provide synthetic rubbers which can be made from carbohydrates, an abundant and reproducible raw material. A still further object is to provide methods for copolymerizing methyl acrylate, ethyl acrylate, and similar alkyl acrylates with various quantities of other monomers including substituted alkyl acrylates, to obtain essentially saturated copolymers which can be vulcanized by certain suitable agents which we have found to be effective. Other objects and advantages of the invention will appear hereinafter.

We have found that synthetic rubbers and rubberlike materials can be made by copolymerizing a mixture of from 80 to 98 percent, by weight, of an alkyl acrylate, which includes alkyl acrylates and alkacrylates such as methyl, ethyl, propyl, butyl, octyl and other alkyl acrylates and methacrylates, with at least 2 percent of either (a) monomers having only one polymerizable double bond, such as aryl acrylates or methacrylates, as for example phenyl and benzyl acrylate, phenyl methacrylate and so forth, or (b) monomers having only one polymerizable double bond ethyl acrylate, cyanoethyl acrylate, methyl chloracrylate, vinyl bromopropionate, bromopropyl methacrylate, bromoethyl acrylate, 3-chloropropyl acrylate, 1,3-dichloro-2-propyl acrylate, bromopropyl acrylate, 2-chloroal1yl lactate, vinylidenechloride, vinyl chloride, allyl chloride, 2- chloroallyl pelargonate, 2,3-dichloropropyl acrylate, di-n-butyl chloromaleate, alpha-chloroacrylonitrile, alpha-chlorostyrene, beta-chlorcethoxyethyl acrylate, chloromaleic anhydride, dimethyl chloromaleate, di-2-chloroethyl maleate, z-chlomethyl-vinyl ether, and so forth. The resulting copolymers are then compounded with a vulcanizing agent and preferably with other compounding ingredients used in the vulcanization of natural rubber, and heated under conditions commonly utilized in the production of natural and synthetic rubber vulcanizates. The vulcanization process of this invention yields satisfactory results when applied to copolymers obtained by polymerization of monomer mixtures containing an alkyl acrylate and a halogen, cyanoor ketonegroup-containing-comonomer, in the proportion, by weight, of from 80 to 98 percent of the acrylate to at least 2 percent, by weight, of the halogen, cyanoor ketone-group-containing comonomer.

Although olefmic unsaturation has usually been considered necessary for vulcanization, the copolymers described herein are essentially saturated, but are vulcanizable by the agents and techniques of the present invention. It is advantageous to vulcanize saturated copolymers, since cross-linkage usually occurs when unsaturated copolymers are made by polymerizing such monomers as butadiene, isoprene, allyl fumarate, divinylbenzene and the like.

Copolymerization can be effected by any method suitable for the production of alkyl acrylate copolymers. Emulsion polymerization is a convem'ent procedure for preparing the copolymers, but these can also be made by solution or mass polymerization. Polymerization can be achieved by the usual methods including the effect of photochemical action or heat polymerization. Although polymerization can be conducted without catalysts or initiators the addition of these greatly speeds up the reaction. The presence of known polymerization regulators such as dodecyl mercaptan, acrylonitrile, carbon tetrachloride, hexachloro ethane, trichloropropionitrile, or alkyl xanthogen disulfides like isopropyl xanthogen disulfide has a beneficial efiect on the process, but vulcanizable copolymers suitable for the production of synthetic rubbers can be made without their use.

The polymerization catalysts or initiators suitable for use in the production of the copolymers of the present invention are, for example, oxidizing agents such as hydrogen peroxide, benzoyl peroxide, sodium perborate, ammonium persulfate, urea-peroxide, percarbonates and other similar substances commonly utilized to initiate or promote polymerization reactions.

When copolymerization is conducted in aqueous emulsion various emulsifying and dispersing agents can be used to effect dispersion of the monomers, improve the stability of the emulsion and reduce duration of the reaction. Suitable agents include: anion active compounds, for example sulfated compounds like sulfated oils such as sulfated castor oil; sulfated alcohols; or alkyl sulfates such as sodium tetradecyl sulfate; sulfonated compounds, like aliphatic sulfonates, for example, the sodium salt of sulfonated petroleum oil; sulfonates of aromatic compounds which may contain alkyl or other aliphatic side chains, for example, the sodium salt of alkyl phenoxyethyl sulfonate and of similar aryl-alkyl sulfonates; cation active compounds like cetyl dimethylbenzyl ammonium chloride and other well known emulsifying and dispersing agents used either singly or in combination in emulsion polymerization.

The polymerizations can be carried out for example in a round-bottomed three-necked, Pyrex glass flask fitted with a thermometer well, a reflux condenser and a stirrer. The monomer mix ture is added to water and an emulsifying agent in the flask, stirred, and heated to about refluxing temperature. The desired amount of catalyst is then added either all at once or by increments.

Heating is applied, if necessary, to maintain gentle refluxing, and the course of the polymerization is followed by noting changes in the refluxing temperature. When refluxing ceases in spite of continued heating (usually at about C.) the polymerization is complete. The emulsion can then be steam distilled to remove monomers and other volatile materials, is coagulated by addition of a dilute solution of sodium chloride, and the polymeric material washed with water and dried.

Data on some polymerizations are given herefollowing classes of vulcanizing agents utilized in the vulcanization of natural rubber and of certain synthetic rubbers.

1. Sulfur, preferably used in conjunction with at least;one vulcanization accelerator, that is a substance known to promote the sulfur vulcanization of natural rubber. Suitable accelerators include, for example, the following types of rubber vulcanization accelerators: Aldehyde-amines like the butyraldehyde-aniline, formaldehyde-monoethylamine and heptaldehyde-aniline condensation products; guanidines like diphenylguanidine; thiazoles such'as mercaptobenzothiazole, benzothiazyl'disulfide, zinc benzothiazyl sulfide, dinitrophenyl benzothiazyl sulfide admixed with diphenylguanidine, cupric salt of mercaptobenzothiazole, thiuram sulfides like tetramethyl thiurammonosulfide and disulfide, or di-N-pentamethylene thiuram tetrasulfide; dithiocarbamates such as N-pentamethylene ammonium pentamethylene dithiocarbamate, selenium diethyldithiocarbamate, zinc dimethylor zine dibutyl dithiocarbamate, ZA-dinitrophenyl dimethyl dithiocarbamate and cupric diethyldithiocarbamate, sodium salt of dibutyl dithiocarbamic acid and other rubber vulcanization accelerators like the reaction. product of carbon bisulfideand methylene dipiperidine, alkyl phenol sulfide, etc.

2. Quinone derivatives described in U. S. .Patent 2,170,191 such as quinone dioxime and quinone dioxime esters of aliphatic and aromatic acids, such as benzoquinone dioxime, which may be used in combination "with suitable oxidizing agents, for example, red lead, or in the form of their oxidation products as exemplified by the vulcanizing agent comprising polymerized dinitrosobenzene as the active ingredient.

3. Dinitrobenzene used either singly or in combination with litharge.

4. Peroxides, such asbenzoyl peroxide and so forth.

In addition to the above-listed natural rubber vulcanizing agents, the alkyl acrylate copolymers of the present invention are vulcanized by the action of amines and amine-condensation products, for example, triethylene tetramine or triethyl trimethylene triamine. When used as the sole vulcanizating agent these amines effect rapid vulcanization of the alkyl acrylate copolymers; where used in combination with natural rubber vulcanizing agents these amines or amine condensation products accelerate the curing process and have a beneficial effect on the resulting vulcanizate.

Data on some vulcanization procedures are shown in Tables II, IV, VI, VIII, XI, XIV,- XVI and XVII, and the properties \of the resulting vulcanizat-es are shown in Tables III, V, VII, IX, XII, XV, XVII, and XIX.

The compounding ingredients listed in Tables II, IV, VI, VIII, XI, XIV, XVI,-and XVIII include in addition to the aforementioned vulcanizing agents and accelerators other compounding ingredients commonly utilized in the production of natural and synthetic rubber vulcanizates to alter the chemical and/or physical properties of the finished product. Thus, for example, carbon black is used as a reinforcing agent; zinc oxide and in some instances litharge or magnesia may be added to render certain accelerators fully effective. Stearic acid and similar softening agents are used as processing aids.

In preparing the vulcanizates the compounding ingredients were milled into the copolymers on a standard rubber mill which had steam-heated rolls.

ucts (vulcanizates) were soft, flexible, elastic,.

rubberlike in appearance andfeel, insoluble in hydrocarbon solvents .and water, and resistant to oxygen, aging andheat.

The practice of the. invention is not limited to the agents shown in the following tables. For example many emulsifiers can be used instead of alkyl sodium sulfate, and various peroxides and per compounds. can be used to initiate the polymerizations.

Other esters of acrylic acid in addition to those shown in the foregoing mentioned tables, which were used to prepare essentially saturated and vulcanizable alkyl acrylate copolymers include, methyl acrylate, propyl acrylate, butyl acrylate and other alkyl acrylates.

Vulcanizates having similar properties were produced by preparing the corresponding copoly mers and subjecting them to vulcanization using procedures similar to those shown in the follow ing tables.

The discovery that halogen, cyano, ketone (CI-I2CO-), and similar groups can be used instead of olefinic linkages to facilitate vulcanization has broad application. For example, bromine atoms in a copolymerchain also act as active centers in vulcanization processes.

Reinforcing agents, fillers, accelerators and. similar rubber compounding ingredients can be added to the copolymers on a rubber mill or any suitable mixer, or the ingredients can be incorporated in the emulsion or solution of the copolymers. Solutions of the copolymers containing'vulcanizingagents, accelerators and so on, are useful as adhesives and rubber cements.

This invention is a valuable advance in the art as it extends the known range of synthetic rubbers, and provides new substitutes for rubher which have in some respects advantages over natural rubber products.

Furthermore, the synthetic rubbers described herein can be made almost entirely (through lactic acid as an intermediate) from carbohydrates, an abundant, domestic, and reproducible raw material.

Although in the specific examples illustrative of preferred embodiments of our invention, synthetic rubbers are produced by conducting vulcanization in the presence of vulcanizing agents used in conjunction with vulcanization accelerators or promoters and conventional compounding ingredients of natural and synthetic rubber vulcanizates, such synthetic rubbers can be obtained in accordance with the method of our invention by subjecting the copolymers to vulcanization in the presence of only a vulcanizing agent.

In the present specification and claims the term vulcanizing agent is meant to include triethylene tetramine, triethyl trimethylene triamine and equivalent amines and amine conden sation products, as well as known rubber vulcanizing agents of the four types listed herein.

The following examples shown in tabulated form are illustrative of the invention. In all of these examples, the physical properties of the final products were'determined by the procedure of the A. S. TvMrspecification D-412-41.

Yield 0f mer, Per Cent hrs.

Water, Temp, Time, Copoly- Persulfate Shore A Hardness Alkyl Sodium Ammonium Sulfate (Emulsi- (Catalyst), g.

fier), g.

Elongation at break,

Per Cent TABLE I Acrylonitrile, g.

Tensile strength, 1bs./sq. in.

Preparation of acrylic resins Amount 7.5 g. ""ifs'i' TABLE III Comonomer r ate.

Methyl Carbitol A rylate.

late.

Example N 0.

Ethyl Acry- Iate, g.

142. 5 Benzyl Aerylate-.- 142.5 142. 5 Beta-Chloroethyl Ac- 95.0 Phenyl Acrylate. 1425 142.5 Beta-Cyanoethyl Ac Physical properties of vulcanisates of Table II 10 TABLE IV Vitleaniedtionof ethyl acrylate-chloropropyl acrylate 'copolymers Compounding formula in parts per 100 parts of copolymers vulcanization Example No. 7 T T7 x ime, emp., ABODEFGH I JKLM NOP 180 213 240 298 360 i 298 240 r 298 w 298 180 .298 300 298 300 g 298 300 V 298 -i .240 298 4 360 298 240 '298 Norn 1.The alphebetical characters shown underthe' above compounding formula have the following significance:

A-Purified mercaptobnzothiezole. IQ uinone dioxime. v a, v B-Zonc oxide. J-Cnpric salt of mercaptobenzothiazole. CStearic acid. K Cupric'diethyldithiocarbamate. DSuliur. V L-Polyac (polymerized di-nitrosobenzene). l Ii -Carbon black. H v MAn' organic polysulfide (polyethylene polysulfide).

F-Tetramethylthiuram disulfide. N-p-Dmitrobenzene. G-An ester type 'plasticizer. O-Intharge. H+-Red lead PFinely ground calcium carbonate.

'NOTE2Q-Th9 copolymer was made from 95% ethyl eerylate and 5% 3-chloropropyl acrylate. 'No'rn 3.The compounded mixtures were cured in 4 x 4 x 0.23 inch molds.

NOTE 4.'Ihe copolymer used inthe'ebovevulcanizations was prepared from 200 g. or gamina-chloropropyl acrylate, 4,000 ml. of ethyl acrylate, 5,000 ml. of water, 80 g. of sodium e1k y l sulfat 40 8 Dfithe sodium salt of aryl alkylpolyether sulfonateend 0.035 g. 'ofamr'nonium persuliate. The polymerization was'earried out at ab'ontfrom 82? to 0. and was finished in about 3 hours. NOTE 5.Ihe ester type plasticizer mentioned under G is a glycol di-octoate.

TABLE v Physical properties of vulcanieates of-Table IV Permanent Permanent Tensile Modulus Ultimate V e Example No. Strength, 7 at 600 Elongation, gigsgig g g i set 0 lbs/sq. in. Per Cent "Per Cent 1, 210 830 m0 s 1, 170 1, 080 (:90 i 806 1, 190 730 690 822 880 490 880 v 774 1, 530 1, 450 650 994 1, 490 660 940 1, 400 1, 370 1, 070 740 1, 014 1, 440 990 790 1, 133 1, 460 1, 180 700 1, 022 980 370 920 902 1; 340 "560 750 l, 280 1, 240 610 780 TABLE V1 Vulcanieaiioitof fidlogen lc'on tainin g acrylic resins v Compounding Forozgggigfrts per parts of vulcanization i gP Monomers grams A B 0' D E F" G H I .T K L 2%? Eth yl Ae late 2 2 29s 2-Bromoet yl Aerylate 3 '1"; 298 3-Ohloropropyl Acrylate" 2 2 60 298 {Ethyl Acrylate 3-Chloropropyl Acrylate. 2 30 298 A(lol'yo?kfilei i 3 ...L 30 10 2 120 298 nc y cry a e {3-Chloropropyl Acrylate- 3 30 10 n-ButylAcrylate 2 30 1 Ethyl Aorylate 3-Ghl0ropr0py1Acrylate 3 l0 2 60 298 Ethyl Aerylatequn, s 2 2 0 298 3-Ohl0ropropy1 Acrylateu 3 1 I .5 so 298 ff f -2 1o 30 29s }3-Chl0ropr0pyl Acrylate... g 1 1 5 f I 1 The elpl n hetica lehgricters shown hereunder have the following significance:

AP urified'uiercaptobenzothiazole. E-Oarb'on black I-Special furnace reinforcing black. B 1110 oxide. F-Tetta'n'lethylthruram disulfide. .TPolyao. C teari'cacid. GvR edlead.

4 V K-Triethylene tetramine. 'D-Sulfur. H'Qu'1none 'dioxime. L-Oalcined magnesia.

Having thus described our invention, we claim:

1. A process of preparing a synthetic rubber comprising compounding a copolymer prepared from a mixture containing, as monomeric components, alkyl acrylate and methyl vinyl ketone in the proportion of from 80 to 98 percent of acrylate to at least 2 percent of the ketone, with sulfur and heating the compounded mixture to effect vulcanization.

2. A process of preparing a synthetic rubber 10 comprising compounding a copolymer prepared from a mixture containing, as monomeric components, alkyl acrylate and methyl vinyl ketone in the proportion of from 80 to 98 percent of acrylate to at least 2 percent of the ketone, with a vulcanizing agent selected from the group consisting of sulfur and the combination of quinone dioxime and red lead, and heating the compounded mixture to effect vulcanization.

WILLIAM C. MAST. CHESSIE E. REHBERG. CHARLES H. FISHER.

18 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,121,134 Rohm Dec. 15, 1914 2,105,361 Nowak Jan. 11, 1938 2,324,935 Kautter et a1 July 20, 1943 2,405,008 Berry et a1 July 30, 1946 2,416,878 Lindsey et a1 Mar. 4, 1947 2,419,221 Kenyon et a1 Apr. 22, 1947 2,442,330 Fuller June 1, 1948 2,451,174 Reuter Oct. 12, 1948 2,492,170 Mast et al Dec. 27, 1949 FOREIGN PATENTS Number Country Date 498,383 Great Britain Jan. 3, 1939 OTHER REFERENCES Mast et al.: vulcanization of Saturated Acrylic Resins, article in Ind. Eng. Chem, vol. 36, pages 1022-1027 (November 1944). 

2. A PROCESS OF PREPARING A SYNTHETIC RUBBER COMPRISING COMPOUNDING A COPOLYMER PREPARED FROM A MIXTURE CONTAINING, AS MONOMERIC COMPONENTS, ALKYL ACRYLATE AND METHYL VINYL KETONE IN THE PROPORTION OF FROM 80 TO 98 PERCENT OF ACRYLATE TO AT LEAST 2 PERCENT OF THE KETONE, WITH A VULCANIZING AGENT SELECTED FROM THE GROUP CONSISTING OF SULFUR AND THE COMBINATION OF QUINONE DIOXIME AND RED LEAD, AND HEATING THE COMPOUNDED MIXTURE TO EFFECT VULCANIZATION. 